We should care but at the same time he’s a politician so had to be seen to not isolate any other friends and allies. From his stand point it’s convenient for us to stay in. He doesn’t want anything to rock the global economy as the US’ economy us just as fragile as anyone’s, he doesn’t want anything upsetting Europe at a time when far right groups are popular and any fissures in the established relationships could be exploited by Putin. And he doesn’t want to P off his other European allies like France and Germany. He’s only got his own best interests at heart and did not make that statement as a caring and concerned friend. As many have pointed out, if the shoe was on the other foot and the US were having to accept rules and governance from Mexico or Canada then they he would be looking to exit ASAP.
From a trading perspective in the long term the US will become less important as will the EU as 80% of the worlds population allive in the developing world. We need to start sucking upto the Chinese, Indians, Africans etc. Big time. The question is are we better off doing that as part of the EU machine or by ourselves?